Dylan Arndt expected to be sitting in the audience for his first show at The Muny.
But the 17-year-old alto sax player found himself on the outdoor stage with 51 other members of the O'Fallon Township High School Marching Panthers.
The band performs in a parade scene in the musical "Hello, Dolly!" which runs through Sunday in Forest Park.
"It was incredible," Dylan said after Monday's opening night. "It was such a massive crowd."
The band got a standing ovation from the 7,000-person audience for its rendition of the song "Before the Parade Passes By."
But Dylan's favorite part has been witnessing all the behind-the-scenes activity.
"We get an intercom call in the room where we're waiting," he said. "And then we come out and see all the actors and singers and dancers warming up and doing costume changes and then running back on stage. It's very busy."
David Lewis, 16, is playing mellophone in the show, although he normally serves as a drum major.
David enjoyed meeting actor John O'Hurley, who plays Horace Vandergelder, the gruff, "half-a-millionaire" owner of a hay and seed company.
O'Hurley is best known for his role as J. Peterman on the 1990s sitcom "Seinfeld." He competed during the first season of "Dancing with the Stars" in 2005 and hosted "Family Feud" from 2006 to 2010.
"I met him, and I got my picture taken with him," David said. "He's a really cool guy. He's relaxed, he's funny and he's super kind."
This year is the 50th anniversary of "Hello, Dolly!" Carol Channing starred in the original Broadway production, which won 10 Tony Awards.
The 1969 movie with Barbra Streisand earned seven Academy Award nominations.
It's described as "the irresistible story of matchmaker extraordinaire Dolly Levi as she 'meddles' her way from Yonkers to New York City."
The last scene in the first act is set during a New York City parade in the early 1900s.
The Muny's creative team brainstormed their way into the idea of using a live marching band.
"We wanted something grand and beautiful and exciting and surprising for the audience," said Mike Isaacson, artistic director and executive producer.
The team turned to the Marching Panthers, which had performed in "The Music Man" in 2009.
The band has been extremely busy this year. They played at Carnegie Hall in New York May and are preparing for the Tournament of Roses Parade in California on New Year's Day.
But O'Fallon Director of Bands Melissa Gustafson-Hinds agreed to take on "Hello, Dolly!" as a volunteer project.
"I thought, 'They will be on stage with superstars, and they'll be performing in front of thousands of people every night,'" she said. "I just couldn't pass it up. It's a huge undertaking, but it's a great opportunity."
Gustafson-Hinds picked 52 of the band's 230 members for the show based on skill and commitment.
They had to spend hours practicing at school and at the theater with The Muny pit orchestra. Isaacson was pleased with the result.
"It's spectacular," he said after opening night. "It's unbelievably joyous. The audience cheered these kids."
Gustafson-Hinds got help with arrangements from the school's percussion director, Evan Hinds, who also is her husband; and Band Assistant Connor Blankenship.
Students are wearing red, white and black period band uniforms provided by The Muny. They're using the school's instruments or their own.
The highlight for Devon Karbach, 17, a bass clarinet player, was marching out on stage opening night and seeing the crowd clap, cheer and go "crazy."
"It's been one of the best experiences of my life," he said. "I don't know if there are even words to describe it."
At a glance
What: "Hello, Dolly!"
Where: The Muny in Forest Park
When: 8:15 p.m. daily through Sunday
Admission: $14 to $85
Tickets: Visit metrotix.com or call MetroTix at 314-534-1111 or The Muny box office at 314-361-1900, ext. 550
Information: Visit muny.org or call 314-361-1900